Proteolipid has been identified as the nucleator of microbiologic calcification. Calcifiable proteolipid has also been isolated from human dental calculus and marmoset bone matrix. Although proteolipids occur in a wide variety of animal and plant tissues, not all tissues are calcified. This research will examine the role of proteolipid in biologic calcification. The proteolipid dependency of vertebrate calcification and whether calcifiability of a tissue is due to specific types of proteolipid or to the biochemical environment of the proteolipid will be determined. Calcification of epiphyseal cartilage will be developed as an experimental tool for studying the qualitative and quantitatve changes in proteolipid during progressive mineralization. Biochemical and histochemical sub-tissue localization of proteolipid in hypertrophic cartilage will provide insight into the role of proteolipid in the local mechanism of calcification. By examining changes in proteolipid concentration, ratios of proteolipid to cholesterol and tissue phospholipids and alteration in the proteolipid, itself, a better understanding of the functional role of proteolipids and membranes in biologic calcification will be attained. Vitamin D-deficient rickets provides a model for studying the role of proteolipid in the transition of cartilage from a non-calcifying tissue to an actively calcifying one. Whether the effect of vitamin D therapy is to promote calcification by regulating synthesis of membrane proteolipid and/or incorporation of specific fatty acid esters, will be determined. The proposed research will also determine whether proteolipids, particulary calcifiable proteolipids, are antigenic. Immunochemistry will be used to determine structural homology among and between calcifiable and non-calcifiable proteolipids. Immuno-electron microscopy will be used to localize proteolipid in calcifying matrices.